The servers for Big Farm are all set out according to country. The exception to that is the International server which is for all nationalities.
As you log into your game, at the bottom of the log in screen is a flag and the server that you are on. If your flag shows the English flag with United Kingdom showing, then that is the server that your farm is on. This is important for two reasons.
Firstly, to log into your farm, you need to make sure that the server is the correct one that you are trying to log into or you can end up starting a new farm on a different server. A lot of members that do this find it really disheartening and confusing when it happens to them and so it is a good idea to ensure that you know what server your farm is on.
The other reason it is a good idea to know what server your on is when you are looking for a cooperative on the Big Farm forums. You can only join a cooperative which is located on the same server as your farm is due to the servers not interconnecting with each other. So a member who has a farm on the EN (United Kingdom) server, can not join a cooperative that is on the US (United States) server.
When you are on the forums, you can tell what server your farm is on by the automatic signature that is set when you first post on the forum. It will have your account name @ server. For example: a member with a farm on the US server with the account name of FarmerBob will have a signature that looks like FarmerBob @ us 1.